The present invention relates to a method and an apparatus for detecting contact between the hand(s) of a driver and the steering wheel of a motor vehicle.
The detection of whether there is contact between the driver's hands and the steering wheel (referred to as “hands-on-off” detection for short) is becoming increasingly important in view of the increasing spread of sophisticated driving assistance systems, such as lane-keeping assistance systems. Typically, these systems are only intended to assist or supplement the driver's actions, but are not designed for autonomous control or to replace the actions of a driver who no longer exerts any control of the vehicle (such as if the driver has released the steering wheel of the vehicle). In the presence of such assistance systems, however, the driver may become particularly tempted to over-rely on the system and undesirably release the steering wheel. Therefore, in operating such assistance systems, it is desirable to check whether at least one of the driver's hands is in contact with the steering wheel whereby the driver is ready to manually intervene if necessary.
If the driver's hands are not detected as being in contact with the steering wheel, various remedial actions can be taken. For example, the driver could receive an optical and/or acoustic warning, the assistance systems could switch off (possibly with a certain delay), and/or the vehicle could be automatically braked in a controlled manner while keeping to the lane and switching on the hazard warning lights. In this regard, the “hands-on-off” detection can be used to enable a “dead man's switch” of the type used in rail vehicles which operate at certain intervals in order to ensure that the driver is alive, is awake, and can react to environmental stimuli.
The detection of a hands-on state is easily made during times when the driver carries out active steering movements. Such movements can be detected by the steering angle and steering force sensors which are usually present in connection with other driving dynamics systems. However, detection becomes more difficult during times when no relatively great manual steering interventions are necessary (e.g., on relatively long, straight stretches or when automatic steering assistance systems are engaged). In these situations, manual engagement with the steering wheel may be very light (e.g., only a finger on the driver's hand may be holding the steering wheel). In any case, it is necessary for the “hands-on-off” detection to be effected in a very reliable manner. Any amount of driver engagement with the steering wheel (including slight steering movements using only a finger on a straight road, or times when the driver is holding the steering wheel substantially motionless) should still be detected as a “hands-on” state.
U.S. Pat. No. 7,109,862 discloses detecting the driver's hands on a steering wheel using an electronic circuit based on a change in the capacitance in a resonant circuit (i.e., acting as a proximity switch). However, such proximity switches require appropriate electrodes, interconnecting wiring, and a controller. In U.S. Pat. No. 7,109,862, these can be integrated with the heating wires of a steering wheel heater. However, steering wheel heaters are not a widespread feature in commercially available motor vehicles. Furthermore, capacitive sensors are relatively unreliable and often cannot determine whether the hands are actually in contact with the steering wheel or are just in the vicinity of the steering wheel.
It would be desirable to provide a method and an apparatus for detecting contact between any portion of the driver's hands with the steering wheel of a motor vehicle which distinguishes between “hands-on” and “hands-off” states in a particularly reliable manner without the need for additional hardware.